Field of the Invention
The present invention relates to a MIS-type semiconductor device having a gate insulating film formed of ZrOxNy (zirconium oxynitride) on a semiconductor layer and a gate electrode on the gate insulating film, with a gate applied voltage of 5 V or more.
Background Art
With further miniaturization of semiconductor devices in recent years, thinner gate insulating film of transistor is in demand. However, there is a problem that when the conventionally used SiO2 film is thinned, the leak current increases. Therefore, a high-k (high dielectric constant) material is used instead of SiO2. A high-k material includes HfO2, ZrO2, TiO2, HfOxNy, ZrOxNy, and others. Specifically, a MIS (Metal-Insulator-Semiconductor) type semiconductor device having a gate insulating film formed of ZrOxNy is disclosed in Patent Documents 1 to 5.
Patent Document 1 discloses a semiconductor device having a gate insulating film on a semiconductor substrate and a gate electrode on the gate insulating film, wherein the gate insulating film is formed of Zr2ON2 or ZrO2-2xN4x/3 (where ⅜<x<¾). The gate insulating film is single crystal or polycrystal. The Zr2ON2 gate insulating film is formed by sputtering a Zr2ON2 ceramic target. Argon is used as a sputtering gas, a substrate temperature is from 600° C. to 800° C., and a sputtering gas pressure is from 0.5 Pa to 0.2 Pa.
Patent Document 2 discloses a MIS-type semiconductor device having a gate insulating film formed of ZrO2 containing nitrogen, wherein the nitrogen concentration of the gate insulating film is higher on the channel side than on the gate electrode side, and the nitrogen concentration of the gate insulating film on the channel side is 1020/cm3 to 1021/cm3. The gate insulating film is formed by sputtering in a mixture gas of nitrogen and oxygen diluted with argon gas at a temperature from room temperature to 800° C. and a pressure from 0.1 mPa to 1 kPa. There is no specific description of which state the gate insulating film is in: single crystal, polycrystal or amorphous.
Patent Document 3 discloses a MIS-type semiconductor device in which a chemical oxide layer, a high-k dielectric layer, a lower metal layer, a capturing metal layer, an upper metal layer, and a polycrystalline semiconductor layer are sequentially deposited on a semiconductor substrate. Si or Group III-V semiconductor may be employed as a semiconductor substrate. The high-k dielectric layer may be formed of ZrOxNy (0.5≦x≦3, 0≦y≦2). There is no specific description of which state the high-k dielectric material is in: single crystal, polycrystal, or amorphous. The high-k dielectric layer may be formed through CVD or ALD. However, there is no specific description about the formation of the high-k dielectric layer by sputtering.
Patent Document 4 discloses that in MISFET, a gate insulating film is formed of ZrOxNy, by sputtering a Zr target in an atmosphere of mixture gas of oxygen and nitrogen introduced into argon.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2005-44835
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2005-217159
Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2011-3899
Patent Document 4: U.S. Patent Application Publication No. 2003/0205772 A1
Patent Document 5: Japanese Patent Application Laid-Open (kokai) No. 2013-135055
The inventors have studied the miniaturization of the MIS type power device by employing a high-k dielectric gate insulating film formed of ZrOxNy. However, it was found that when the gate insulating film is formed of ZrOxNy, the threshold gate voltage shifts due to high applied voltage, resulting in an unstable operation, at certain composition ratios x and y of ZrOxNy. Therefore, the inventors of the present application developed a technique disclosed in Patent Document 5 in order to solve the above problem. Moreover, they found an optimized range of the oxygen composition ratio x and the nitrogen composition ratio y in the gate insulating film formed of ZrOxNy, with less shift in threshold voltage than the relationship between the oxygen composition ratio x and the nitrogen composition ratio y disclosed in Patent Document 5.